The present invention relates to a magnetic head demagnetizer, in particular, relates to such a demagnetizer which is mounted in a tape cassette. This kind of prior art head demagnetizer is shown in the Japanese patent publication 10765/83.
FIG. 5 shows a prior head demagnetizer which is mounted in a tape cassette 1. The tape cassette 1 has a pair of holes H.sub.1 and H.sub.2, and an erasing head 7. The tape cassette 1 is positioned in a magnetic tape recorder which is subject to erasure. The tape cassette 1 is positioned so that the holes H.sub.1 and H.sub.2 are engaged with spindles of a tape recorder, and then, the erase head 7 touches with a magnetic head 15 which is subject to erasure.
However, a demagnetizer of FIG. 5 has the disadvantage that it is sometimes not applicable to a particular structure of a magnetic tape recorder. That is to say, lately there are cassette tape recorders, which are for instance mounted on a vehicle, that function to prevent the loosening and/or twisting of a tape. Those tape recorders have a magnetic recording/reproducing head which is first shifted from a normal position. In operation of those kind of tape recorders, a tape is first wound up so that a tape has some tension, then, a recording/reproducing head is shifted so that it contacts with a tape for recording and/or reproducing operation.
When a head demagnetizer of FIG. 5 is mounted in that kind of tape recorder, a spindle of the tape recorder would first rotate so that a tape has tension. However, since it is a demagnetizer that is mounted on the tape recorder, not a cassette tape for recording/reproducing, the initial wind up operation for providing tape tension does not finish, and the spindle rotates needlessly. And, since the erase head 7 does not contact with the magnetic head 15 because of the absence of tension on a tape, the magnetic head 15 can not be erased.
FIG. 6 is another prior head demagnetizer which solved the above problem. In FIG. 6, the numeral 1 is a cassette holder, 7 is an erase head, 15 is a magnetic head which is subject to erasure, 2C and 2D are reels, and 20 is a cleaning tape which runs between the reels 2C and 2D through the face of the heads 7 and 15. The cleaning tape 20 functions to clean the magnetic head 15 by sweeping the face of the head 15.
In operation, when the cassette holder 1 is mounted in a tape recorder, a spindle of the tape recorder rotates to provide tension on a tape. Since a cleaning tape 20 is provided in the cassette holder 1, the cleaning tape 20 has tension and the tape recorder recognized that the tape has tension, then, the magnetic head 15 is shifted so that it touches with the erase head 7. Therefore, the erasing operation is carried out normally.
However, the head demagnetizer of FIG. 6 has the disadvantages that the life time of a cleaning tape is short, and the erasing operation is not reliable since a cleaning tape exists between the erase head 7 and the magnetic head 15 not only in the cleaning operation but also in the erasing operation. Because of the short life time of the cleaning tape, the head demagnetizer itself has the short life time which is the same as that of the cleaning tape.